1. Field of the Invention
The present invention relates to an engine revolution controlling apparatus and particularly to an apparatus for controlling the revolution of an engine in relation to loads.
2. Description of the Related Art
Most engine generators for use as alternating current sources have increasingly been provided with an inverter for stabilizing the output frequency. Such an engine generator is driven by an engine to generate an alternating current which is converted into a direct current and then supplied to an inverter for output at a commercial frequency. The output of the generator linked with the inverter is hardly affected in the frequency by the number of revolutions of the engine and can thus be determined corresponding to the load by controlling the number of revolutions of the engine.
For example, an inverter system engine generator is disclosed in Japanese Patent Laid-open Publication (Heisei)5-18285 where the load is detected from a current output of its inverter and used for controlling the throttle opening in the engine. This controlling manner allows the voltage output of the generator to remain substantially uniform regardless of any fluctuation in the load.
More specifically, a control signal is generated by a central processing unit (CPU) from a difference signal between the target number of revolutions and the current (actual) number of revolutions and a signal representing a changing speed of a number of revolutions and then used for controlling the throttle opening to provide a desired amount of fuel. The applicants, have developed and proposed a controlling apparatus for an engine which drives a generator where the throttle opening is controlled or varied so that the conduction angle of semiconductors in a converter for rectifying the alternating current output of the generator remains at its predetermined level (as disclosed in Japanese Patent Laid-open Publication (Heisei)11-308896).
The conventional controlling apparatus for an engine includes a table which carries a list of parameters for calculating a desired level of the throttle opening. The desired level of the throttle opening in the table is determined from the difference signal and the changing speed signal of the revolutions.
For controlling the operation of the engine with the use of the table in consideration of any load to the engine, a procedure of processing various data or parameters including the throttle opening is necessary. As the number of parameters increases, the table becomes large in the size and intricate in the architecture. This increases a load to the CPU (providing difficulties for the controlling action). As a result, the controlling action for stabilizing the operation of the engine in consideration of the load will decline the stability. Also, if the CPU is loaded with too many data to be processed, its action may disturb another controlling action. For avoiding such a disturbance, the CPU itself has to be improved in the speed of operation for increasing the processing capability.
The present invention has been developed in view of the above aspects and its object is to provide an engine revolution controlling apparatus which can ensure a stable action of the engine in consideration of any load without increasing the load to the CPU.
The first feature of this invention is an engine revolution controlling apparatus having a fuel supply controlling means for controlling a supply of fuel so that a difference between the actual number of revolutions and the target number of revolutions in the engine is converged at zero, characterized wherein the fuel supply controlling means comprises a throttle valve driven by a stepping motor and a central processing unit for calculating a control quantity of the stepping motor, the central processing unit including a means for correcting the difference between the target number of revolutions and the current number of revolutions with an adjustment based on a difference between the current number of revolutions and the previous number of revolutions and a difference between the previous number of revolutions and the number before previous number of revolutions and a means for determining the control quantity based on the corrected difference.
According to the first feature, a control quantity is calculated based on the target revolution of the engine, actual revolution, and past engine revolutions. The control quantity is calculated based on the parameters by using arithmetic operation with the equations.
The second feature of this invention is that the central processing unit includes an adjustment calculating means for dividing the control quantity by a subtraction of at least a function of either the throttle opening or the actual number of revolutions of the engine from a predetermined gain. According to the second feature, the control quantity is corrected responding to the load which is represented by the throttle opening and the target number of revolution of the engine.